Froth-crowding flotation machine and method



y 31, 1956 M. J. SAYERS 2,756,877

FROTH-CROWDING FLOTATION MACHINE AND METHOD Filed Aug. 18, 1952 2 Sheets-Sheet l 31mm or:

MARSHALL J. SAYERS M. J. SAYERS July 31, 1 956 7 FROTH-CROWDING FLOTATION MACHINE AND METHOD Filed Aug. 18, 1952 2 Sheets-Sheet 2 Zsnventor: MARSHALL J. SAYERS i by mechanical action.

United States Patent FROTH-CROWDIN G FLOTATI'ON METHOD Marshall J. Sayers, Salt Lake City, Utah, assignor to The Galigher Company, Salt Lake City, Utah, a corporation of Utah Application August 18, 1952, Serial No. 304,943

4- Claims. (Cl. 209-168) I This invention relates to aeration machines of the type utilized'in froth flotation practices, andknown generally as flotation machines. It is particularly concerned" with improvements which make such machines betterable to handle what are commonly termed brittlefroths, and includes, also, the method of handling such froths.

Practically all presently used types of flotation machines produce, as an end product, a mass of froth which is laden with material particles selectively picked up from the flotation pulp within a dynamically maintained bubble column. This mass overlies the bubble column, and continuously discharges quantities of froth over afroth-overflow lip into a suitable launder as the froth is continuously replenished from the aerated pulp below.

The maintenance of and proper discharge from such mass of froth are of critical significance'in'the operation of any flotation machine, since factors operative there are of considerable importance in determining the degree of metallurgical or other recoveries made from any given run of pulp, as well as, in many instances, theextent of consumption of expensive chemical reagents.

The character of the froth necessarily differs considerably in various aspects of flotation practice. Because of differences in particular materials treated from time to time and of reagents employed in particular flotation processes, it is not always possible to produce. a tough and durable froth. Often the froth has a so-called brittle character, meaning that it breaks down and drops the values which it carries before it can be taken off'from the body of pulp proper. The art'of flotation has longbeen plagued with froths of this nature in particular instances. The remedy, if any, has usually been the use of considerably more than normal quantities of a frothing reagent, or the use of special, relatively expensive reagents.

Recently, difficulty was encountered with. a. particular installation of flotation machines in the. floating of a certain ore pulp subject to over-flocculation. Excessive quantities of frothing reagent were required to maintain standard recoveries, since the froth was of a highly brittle character.

The particular machines involved in that instance were the subaeration type manufactured by the Galigher Company of Salt Lake City, Utah, under the proprietary trademark Agitair.

In a subaeration type of flotation machine, a rotating impeller which is completely or largely. submerged'in the pulp, serves to diffuse a supply of air throughout the pulp The Agitair may be regarded, for the purpose of this invention,,as typical of subaeration machines having an impeller fixed to the lower end of an elongate, vertical shaft which extends upwardly Patented July 31, 1956 ice through the body of pulp in an open-topped flotation tank and which is rotated during operation of the machine.

In attempting to overcome the difliculty above referred to, without the expense of abnormal quantities of frothing reagents, I conceived of and built an arrangement of crowding baffles, which, to my surprise, not only brought operation back to the sought for standard by the use of normal quantities of frothing reagent, but which even enabled standard recoveries to be obtained with less than normal quantities of the frothing reagent. Observation over an extended period of experimental use has definitely proven the'practical value of this crowding baflle structure.

Generally speaking, it is desirable in any flotation machine'that the froth be directed or guided to a certain extent in its build-up at the surface of the bubble column. Baffles or crowding boards have long been used for this purpose. For example, the Agitair flotation machine has heretofore been constructed in the form covered by Booth U. S. Patent No. 2,182,442, where it possesses frothdirective baflles, or crowding boards, arranged directly behind the froth overflow lips, for crowding the froth away from the impeller shaft and toward the overflow lips as the froth mass builds up at the surface of the pulp body. Nevertheless, known structures of this type have not effectively overcome the dilficulties encountered with brittle froth.

An essential concept of my invention is that there should be a marked reduction in the effective length of the froth overflow structure, accompanied by a build-up in height of the froth mass and a gradual reduction,.upwardly, in the cross-sectional area thereof, to a point-Where the exposedsurface of the froth mass is effectively reduced over standard practice and an effective hydrostatic head of froth is achieved.

I have found that this considerably increases the velocity ofv froth discharge, increases the carrying capacity of the froth to an extent which makes possible the successful handling of extremely fragile froths which result from an over-flocculated condition of a flotation pulp, minimizes break-down of fragile or brittle froths, and materially reduces the quantity of frothing reagents otherwise required.

These desired conditionsare obtained, from the'standpoint of machine structure, by providing an arrangement of crowding baflles extending continuously around the major extent of the upper periphery of the customary open container for pulp, and sloping upwardly and inwardly of such container, thereby reducing the area of the open top of the container to less than what-it would normally be and directing flow of froth toward a peripheral gap which defines a froth overflow lip of length shorter than normal.

Procedurally, the froth is substantially pyramided up from the level of and over the area of its origin at the top of the bubble column, to a higher level'having'an effectively reduced area, and is discharged approximately at that higher level and along only a relatively small fractional portion of the periphery of the so massed froth. In effect, then, the froth is crowded into substantially truncated'pyramidal formation having an exposed upper surface of area reduced relative to the normal, and is overflowed from the container along a lip length reduced rela tive to the normal.

Withthis baflle arrangement in machines such as the Agitair, I have found that the fact that the froth is not 3 protected from contact with the rotating impeller shaft, as it is in the aforementioned Booth patent, does not seem to be a disadvantage, possibly because of the considerable reduction in actual frothing requirements resulting from the unique structural and functional features of the invention.

Further objects and features of the invention will become apparent from the following detailed description of the presently preferred specific forms thereof which are illustrated in the accompanying drawings as typical of those various embodiments possible of construction, on the basis of the teachings hereof, by those skilled in the art.

In the drawings:

Fig. 1 represents a perspective view, looking downwardly upon a series of flotation cells embodying the invention, portions of the cell walls being broken away, and the impeller and impeller drive mechanism being removed, for convenience of illustration;

Fig. 2, a central vertical section extending from front to back of one of the cells of Fig. 1, showing the impeller and impeller drive mechanism in place;

Fig. 3, a top plan view of a somewhat different embodiment, showing how the invention is applied in a circular cell, the impeller and impeller drive mechanism being removed; and

Fig. 4, a vertical section taken on the line 4--4 of Fig. 3.

Referring to the drawings:

The individual cells of the flotation machine of Figs. 1 and 2 are of conventional, rectangular configuration, being constructed from structural steel shapes and plates in a fashion which is essentially customary for the aforementioned Agitair machine being presently manufactured by The Galigher Company. In this instance, however, the divider frames 11 between the individual cells 10 are constructed to space and support laterally placed, crowding bafiles of the invention.

In accordance with the invention, an upwardly and forwardly inclined baffie 12 is provided at the back of each cell, rising upwardly from a level in the cell which, in the illustrated instance, is approximately midway between the cell bottom Ida and the froth overflow lip 10b, see Fig. 2. The exact level at which such bafiie 12 originates may vary in certain instances, depending upon the character of the ore being treated and the particular characteristics of the froth.

Such rear or back baffle plates 12 are preferably flat sheets of steel plate. They are advantageously supported by attachment, as by welding, to the rearward ends of opposite side or lateral crowding baffles 13, which are fastened, as by welding, to crossarm members 14 of the respective structural frames 11.

The side or lateral crowding baffles 13 are preferably each formed with an upwardly and inwardly sloping, lower portion 13a, and with a vertical, upper portion 13b, to define, together with the rear or back baffle 12 and the normal vertical front wall ltlc of the cell, an upwardly convergent, froth collection zone 15 having an upper opening at the open top of the cell which is of reduced area with respect to the normal horizontal crosssection of the cell.

The froth overflow lip 10b defines, along its length, a peripheral gap 16 for the discharge of froth from the froth collection zone 15, and, because of the upwardly and inwardly sloping nature of the peripheral bafiles 12 and 13 defining such zone, both the lip and the gap are of shorter than normal length, considering the horizontal cross-section of the cell proper.

The upwardly convergent nature of the froth collection zone 15 and the shorter than normal length of the froth discharge lip 1% produces, in practice, a considerably more stable mass of froth than would otherwise he the case, and a froth discharge at greater than normal velocity. Accordingly, even though the frothfbe of a 4 brittle nature, it is effectively maintained and discharged, with its load of values, by reason of the invention.

With the bafile structure of the invention, no change need be made in the pulp aerating mechanism or arrangement thereof. Thus, in the machine illustrated, the impeller 17, Fig. 2, and the drive mechanism therefor, indicated generally at 18, are constructed and arranged as usual.

In the embodiment of Figs. 3 and 4-, a single cell, embodying a container or tank 20 of circular configuration, is provided with an upwardly convergent hood 21 about the periphery of its open top to define a froth collection zone 22 conforming generally with the froth collection zone 15 of the previously described embodiment.

A shorter than normal froth overflow lip 23 defines a gap 24 in the upper peripheral wall portion 21a of the hood 21, for the velocity discharge of froth in substantially the same manner as with the gap 16 of the previously described embodiment.

In both of the embodiments here illustrated, the upper portion of the peripheral wall formed by the froth crowding baffles or hood, is vertically disposed in the vicinity of the overflow lip to provide for uniform flow characteristics throughout the entire cross-section of flow.

While the circular embodiment of the invention will not be used to the extent that the standard rectangular embodiment will, it exemplifies the various ways in which the concepts of'the invention may be incorporated in and adapted to a variety of particular circumstances of use. It will, accordingly, be realized that various changes may be made in the embodiments here specifically illustrated and described without departing from the scope of the claims which here follow.

I claim:

1. In a froth flotation machine, the combination with an open-topped, bubble-column-defining container for pulp, and means for aerating the pulp within the container, so that bubbles rise through the bubble column and collect in the form of froth on the surface of the pulp, of baffle structure peripheral to the open top of said container and converging upwardly and inwardly thereof through at least a lower and major portion of the height of said baffie structure, thereby defining an upper opening for said container which is of reduced area; and means defining a relatively narrow gap interrupting the peripheral continuity of said baffle structure and a froth-overflow lip for said container intermediate the height of the baffle structure, said lip extending along said gap below the level of the top of said baffie structure, so that a hydrostatic head froth will be crowded above the lip during operation of the machine.

2. The combination recited. in claim 1, wherein the container is rectangular, and the baffie structure is made up of three bafiles corresponding to three sides of the container and extending above the upper ends thereof, the two opposing baflles being substantially similarly formed, and sloping upwardly and inwardly of the container, and the other baffie sloping upwardly and inwardly of the container in intersecting relationship with the two opposing baffles and in opposing relationship to the fourth sides of the container, said bafilcs extending above the said sides of the container so that at least a portion of the length of the said fourth side of the container becomes the froth-overflow lip, and so that the gap is de fined between the said two opposing baffies.

3. The combination recited in claim 2, wherein the two opposing baffles slope upwardly and inwardly of the container through the lower and major portion of their heights, but rise substantially vertically through the upper portion thereof, and the other bafile slopes upwardly and inwardly of the container throughout its height; and wherein the froth-overflow lip extends along the fourth side of the container at a level adjacent the termination of slope of said two opposing baflles.

4.- In froth flotation practice, an improved method comprising the steps of introducing flotation pulp into References Cited in the file of this patent an aeration chamber which defines a bubble column; treating said pulp Within said chamber to produce a mass UNITED STATES PATENTS of brittle froth overlying said body of pulp; peripherally 1,155,836 Owen Oct. 5, 1915 crowding and enclosing said mass of froth to limit the 5 1,346,286 Waterhouse July 13, 1920 surface thereof exposed to the atmosphere and to build 1,478,703 Dolbear Dec. 25, 1923 up a hydrostatic head of froth; and conducting a gravity 1,547,548 Allen July 28, 1925 fiow stream of froth from a relatively restricted area 2,054,539 GutZeit Sept. 15, 1936 of said mass of froth at a velocity attributable to said "2,142,207 Price Jan. 3, 1939 10 2,143,669 Weinig Jan. 10, 1939 hydrostatic head of froth. 

1. IN A FROTH FLOTATION MACHINE, THE COMBINATION WITH AN OPEN-TOPPED, BUBBLE-COLUMN-DEFINING CONTAINER FOR PULP, AND MEANS FOR AERATING THE PULP WITHIN THE CONTAINER, SO THAT BUBBLES RISE THROUGH THE BUBBLE COLUMN AND COLLECT IN THE FORM OF FROTH ON THE SURFACE OF THE PULP, OF BAFFLE STRUCTURE PERIPHERAL TO THE OPEN TOP OF SAID CONTAINER AND CONVERGING UPWARDLY AND INWARDLY THEREOF THROUGH AT LEAST A LOWER AND MAJOR PORTION OF THE HEIGHT OF SAID BAFFLE STRUCTURE, THEREBY DEFINING AN UPPER OPENING FOR SAID CONTAINER WHICH IS OF REDUCED AREA; AND MEANS DEFINING A RELATIVELY NARROW GAP INTERRUPTING THE PERIOHERAL CONTINUITY OF SAID BAFFLE STRUCTURE AND A FROTH-OVERFLOW LIP FOR SAID CONTAINER INTERMEDIATE THE HEIGHT OF THE BAFFLE STRUCTURE, SAID LIP EXTENDING ALONG SAID GAP BELOW THE LEVEL OF THE TOP OF SAID BAFFLE STRUCTURE, SO THAT A HYDROSTATIC HEAD FROTH WILL BE CROWDED ABOVE THE LIP DURING OPERATION OF THE MACHINE. 